The present invention relates to cutting tools and, in particular, it concerns a modular cutting tool assembly in which cutting inserts with different orders of rotational symmetry can be used alternately with a single tool holder.
It is known to employ cutting inserts made of various hard materials which have round, polygonal, or otherwise rotationally symmetric cutting edges mounted in a receiving pocket of a tool holder of a cutting tool. During a machining operation (turning, milling, etc.), only a portion of the available cutting edge typically actually cuts the workpiece. The extent of this portion depends on the depth of cut. When a portion of an indexable cutting edge of a regular (e.g., polygonal) insert has been worked, the insert is indexed to present a whole new cutting edge.
In the case of cutting inserts with polygonal cutting edges, proper operation can only be achieved by rotationally securing the insert within the pocket so as to withstand the cutting forces generated during use. Conventional teaching has relied on abutment surfaces resulting from the inherent polygonal shape of the cutting insert. However, especially in high torque applications, or in polygons with large numbers of sides, the inherent abutment geometry may prove inadequate to withstand torques which may result from cutting forces.
Cutting inserts with round cutting edges exhibit rotational symmetry and could theoretically be continuously indexable in any angular position to accommodate actually observed wear. In practice, however, round inserts have also become restricted to use with a discrete number of indexing stations, angularly spaced by an equal shift angle. The angular shift between the indexing stations is referred to as the "angular pitch" of the insert.
In order to make optimal use of a round cutting insert, it is desirable to prevent rotation of the insert from its indexed position during the cutting process, thereby limiting the wear to a defined portion of the cutting edge. This ensures that the portion of the cutting edge presented after repositioning is, in fact, un-used.
A number of designs have been suggested for anchoring round inserts against rotation. These designs may be subdivided into two types, namely, "seat-pinning" and "lateral abutment". Examples of a seat-pinning design may be found in U.S. Pat. No. 5,296,288 to Flueckiger and European Patent Publication No. 300,172 to Stashko. The lateral abutment design is exemplified by U.S. Pat. No. 3,346,336 to Rescigno. All of these designs suffer from limited torque-resisting capability due to the poor size, location and orientation of the contact surfaces.
As will be clear from the above discussion, the requirements for effective restraining of a cutting insert are typically highly specific to the geometry of the cutting edge. Thus each type of insert, triangular, rectangular, square, or round, is provided with a dedicated tool holder design with a corresponding pocket shape. As a result, the use of multiple insert types is accompanied by the expense of providing and storing multiple tool holders, and necessitates the additional labor of exchanging the entire tool between cutting operations.
In an attempt to reduce these costs and labor, modular systems based on replaceable cartridges have been developed. Examples of such systems include the "Modulmill" system commercially available from SANDVIK Coromant and the "NOVEX F 2010" system commercially available from Montanwerke Walter GmbH. These systems employ replaceable adapter cartridges each of which provides a pocket with clamping geometry suited to a specific cutting insert. Although these systems do allow the primary tool holder to be used with different cutting insert types, the replacement of the cartridges still adds a wasteful additional dissembly/assembly step to the changeover.
There is therefore a need for a modular cutting tool assembly which allows alternate use of multiple cutting inserts with differing numbers of indexing positions within a single tool holder pocket. There is also a need for cutting inserts and tool holders for use in such an assembly.